The invention relates to a configuration and a method for testing a circuit apparatus provided for controlling an occupant protection device of a motor vehicle.
The European Patent EP 0 684 163 B1 describes a circuit apparatus for controlling an occupant protection device of a motor vehicle. An energy storage capacitor is provided in parallel with a series circuit including a first controllable power stage, a triggering element for the occupant protection device and a further controllable power stage. The occupant protection device, which is an airbag or seatbelt pretensioner, is triggered only if the two controllable power stages are turned on. To check the operability of a power stage, a control circuit causes a respective one of the power stages to be turned on for test purposes, while at the same time the other power stage remains turned off, so that the triggering element is not triggered. A respective current sensor is allocated to each power stage. The current determined during the test routine described above allows conclusions to be drawn about the operability of the power stage which is being checked.
Such a series circuit, which has two controllable power stages and a triggering element, takes up a large area, in particular because of the required number of controllable power stages when such a series circuit is implemented as an integrated circuit. As a consequence, such a series circuit is complex and costly to produce.
The Published International Patent Application WO 93/17893 discloses a circuit apparatus for controlling an occupant protection device of a motor vehicle. The circuit apparatus has an energy storage device which is provided in parallel with a series circuit including a triggering element and a single controllable power stage. The occupant protection device, in the form of an airbag or seatbelt pretensioner, is triggered when the controllable power switch is turned on. In such a circuit apparatus it is not possible to check the operability of the controllable power stage, since any driving for test purposes causes the energy storage capacitor to be discharged via the triggering element. The result would be an undesirable triggering of the occupant protection device.
It is accordingly an object of the invention to provide a configuration and a method for testing a circuit apparatus provided for an occupant protection which overcome the above-mentioned disadvantages of the heretofore-known configurations and methods of this general type and which, despite requiring only a small number of components, permit a reliable checking of the operation and a reliable function testing.
With the foregoing and other objects in view there is provided, in accordance with the invention, a configuration for testing an operability of an occupant protection device for a motor vehicle. The configuration includes a circuit apparatus including a series circuit and an energy storage capacitor, the series circuit including a triggering element and a controllable power stage, the energy storage capacitor being connected in parallel to the series circuit for forming a parallel circuit; an energy source for supplying a test current to the parallel circuit; and an evaluator for picking up and evaluating a test voltage dropping in the series circuit, when the energy storage capacitor is at least substantially discharged and the controllable power stage is switched to a conducting state.
In accordance with another feature of the invention, a junction point is provided between the triggering element and the controllable power stage. The energy source has a terminal and the evaluator taps the test voltage between the junction point and the terminal of the energy source.
In accordance with yet another feature of the invention, the evaluator uses a voltage drop across the energy storage capacitor for checking whether the energy storage capacitor is at least substantially discharged. The evaluator switches the controllable power stage into the conducting state for test purposes only if the energy storage capacitor is at least substantially discharged.
In accordance with a further feature of the invention, the triggering element can be triggered by a triggering current that is smaller than the test current.
In accordance with yet a further feature of the invention, the evaluator generates an error signal based on an evaluation of the test voltage.
In accordance with an added feature of the invention, the evaluator, after switching the controllable power stage to the conducting state, switches the controllable power stage to a non-conducting state for test purposes and subsequently picks up and evaluates the test voltage.
In accordance with another feature of the invention, the evaluator picks up and evaluates the test voltage after a given time period, the given time period starting when the evaluator switches the controllable power stage to the non-conducting state.
In accordance with a further feature of the invention, the evaluator generates an error signal based on an evaluation of the test voltage after switching the controllable power stage to the non-conducting state.
In accordance with another feature of the invention, at least one decoupling resistor is connected in series with the parallel circuit.
With the objects of the invention in view there is also provided, a method of testing an operability of an occupant protection device for a motor vehicle or, more specifically, a method of testing a circuit apparatus that is used to control the occupant protection device. The method includes the steps of providing the circuit apparatus, which includes a series circuit and an energy storage capacitor, the series circuit includes a triggering element and a controllable power stage, the energy storage capacitor is connected in parallel to the series circuit for forming a parallel circuit; supplying a test current to the parallel circuit with an energy source; switching the controllable power stage to a conducting state, when the energy storage capacitor is at least substantially discharged; subsequently picking up a test voltage from the series circuit; and evaluating the test voltage.
In accordance with another mode of the invention, the controllable power stage is switched to a non-conducting state after the step of switching the controllable power stage to the conducting state; and subsequently the test voltage is picked up from the series circuit and the test voltage is evaluated.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a configuration and a method for testing a circuit apparatus provided for controlling an occupant protection device for a motor vehicle, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.